Databases

Owners:

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What is a database

• A Database is a collection of interrelated data items, stored once and
  organized in a form for easy retrieval.
• Store and control large amounts of data
• If properly designed it provides a consistent view of the data
• All entities have a relationship between them

Why use a database?

• Reduces programming effort
• Easier to create and modify data (compared to individual files)
• Only need to update one location - one copy of all information

What is a database management system (DBMS)?

• Provides a method of storing and using data in a database
• "Nothing more than a computerized data-keeping system"
• Several types that can be used on z/OS: inverted list, hierarchic, network, and relational

Why are DBMS useful?

• A database stores the data only once in one place and makes it
  available to all application programs and users.
• Data can also be backed up and recovered more easily in a
  single database than in a collection of flat files.
• Databases provide security by limiting access to data. The ability
  to read, write, update, insert, or delete data can be restricted.
• Database structures offer multiple strategies for data retrieval
  (sequentially or go directly to the desired data).
• Finally, an update performed on part of the database is
  immediately available to other applications. Because the data
  exists in only one place, data integrity is more easily ensured.

The role of a DBMS is to provide:

1. Enable concurrent access (I.e. multiple users,
   multiple applications) to a single copy of the data
2. Control concurrent access via a locking
   mechanism with ACID properties (ACID is an
   acronym for atomicity, consistency, isolation, and
   durability) so as to maintain integrity for all
   updates
3. Reduce data redundancy by maintaining only one
   copy of the data
4. Automated rollback, restart and recovery

ACID

• Atomicity - the transaction must execute completely, or
  not at all
• Consistency - Resources must remain consistent (ex.
  Same amount of money debited and credited)
• Isolation - each transaction must appear to occur before
  or after any other transaction
• Durability - If the transaction completes successfully, the
  state (changes due to the transaction) will survive any
  future failures

What is the role of a DBA (Database Administrator)

• Provides standards for databases
• Determines rules for accessing data and monitors its security
• Approves the use of any programs that access production databases
• Controls database integrity & availability; monitors activities for backup and recover
• Guides, reviews and approves database designs

What is DB2?

• Short for database 2
• A relational database produced in 1982 by IBM, was one of the first dbms to use sql
• Relational database has no or little redundancy in data so it can efficiently store large volumes of data
• Significantly slower than ims or idms databases

What Is IMS (Information Management System)

• A hierarchal database produced by IBM in 1972
• Originally designed for the Apollo space program
• Hierarchal system contains redundancy in data but is extremely fast

What Is IDMS

• Uses a network style architecture similar to hierarchal but is slightly more flexible

Database Comparison

Hierarchical vs. Relational Databases

Hierarchical
Storage:
-Parent/Child Relationship
-Less Redundant Data
-Data Duplication
Example:

Data Structure:
-Data Connected in Tiers
-Each tier’s next level up is its parent
-That tier is the next tier’s child
Relational:
Storage:
-Data stored within tables
-Table consists of records and fields
-Records: rows or ‘tuples’
-Fields: columns or ‘attributes’
-Tables are ‘related’ to each other
-Relationships are shown using key constraints
Example:

-Much data duplication on databases in lower normal forms
Differences between Hierarchy vs. Relational Database:
-Operational Data(Relational):
-Analytical Data(Hierarchy):
Example including Object Oriented Programming:
- Basically a Venn Diagram of using: Relational, Hierarchical, and Object Oriented.

Differences with using Relational, Hierarchical, and Object Oriented:
Price/Benefit Analysis:
Hierarchical: Uses design and application logic.
-Price: Hierarchical has a longer development cycle than other 2
-Benefit: Hierarchical has better performance
Example:

Relational: Uses ‘SQL’ for navigation run time.
-Price: Price based on performance
-Benefit: Short and to the point dev cycle
Example:

Object Oriented: Uses method calling to navigate database.
-Price: Development is easier
-Benefit: Constant reuse of methods
Example:



Hierarchical (IMS):
– Data is relatively static (can not just "add a column")
– Navigational : need to know the structure to get to the data
– Faster & more efficient - once Segment Search Arguments (SSAs) are coded

Relational(DB2):
– Changeable info
– Change in structure : no impact on existing application
– Non-Navigational : no need to know the structure right data (just tablename and columnname(s))

Benefits Of Database On A Mainframe

• All data is kept on one system limiting io time

Benefits Of Database On A Distributed System

• Easier to manage on small scale projects

What is SQL?

• Stands for Structured Query Language
• High level language used in programming database
• Three categories
  1. DML: data manipulation language - read and modify data
  2. DDL: data definition language - define, change, or drop DB2 objects
  3. DCL: data control language - grant and revoke authorizations